text:
Does engine oil have a shelf life?
Suppose that I buy a case of oil.  For some reason I stop flying and the oil sits in storage for a sufficiently long time.  After that, I decide I want to put it in my engine.
Is there a point after which (reciprocating) engine oil should no longer be used after being kept in storage?
If the answer is "Yes", what sort of time range is it?  Months, years, decades?

Engine oil in quart plastic bottles is considered to be good for 10 years unopened.
The Exxon document here lists a 10-year shelf life for each of the oil products listed when stored in unopened, undamaged quart containers between 0 and 40 degrees C (32-104 degrees F).

Here's a source.   https://www.exxonmobil.com/en/aviation/knowledge-library/Resources/shelf-Life-Bulletin

I edited that link into the answer & removed my earlier comment. Good find, answers the question nicely.

A friend who flies bush in Canada had a large shed full of aviation oil, a mix of 65, 80 and 100 weight.  It was over 20 years old.  So were the planes he flew.  He talked with the tribologists in London Ont, and was informed that absent oxidation from leaking open containers, they could see no reason why his oil wasn't good.
Most of it was in cardboard cans, rather than plastic bottles. With an abundance of caution, but also with an interest in not wasting valuable motor oil, he sent samples off to the lab for some expensive tests.
About $1400 CDN later, he got reports on the oil from the lab.  The only notable finding was that some of the particulates in the oil had precipitated out, but that was of no consequence.  Since he ran a charter operation the results and a letter went to the manufacturers and they signed off.  So he used the oil.  He had so much that in summer he would put some into his automotive diesel fuel to help with lubricity.
The individual containers did not have a "use by" date.  There was a date code on the cartons.
Environmentally, his oil was exposed to temperatures much colder than 0C, and his oil was easily 20 years old.  On the other hand, it was stored in a shed which provided some protection from the elements.
Perhaps engine oil is like MREs.


text:
A pilot faces a medium-term loss of their medical. What can they expect?
This closely related question asks about what options a pilot has when facing a permanent loss of medical.
However, not all disqualifying conditions are permanent. Maybe you got an interesting disease known for its 7-month contagious period. Maybe you broke an important, slow healing bone. At any rate, whatever silly thing you did to yourself, you will be flying again, but it will take several months.
As a pilot, what options do you have during this period of your career?  Are you likely to be furloughed?  Assigned alternate duties? I'm interested in answers relating primarily to the United States or Europe.

Really need to clarify the question.  From the context, it seems that you mean just commercial pilots, who are a small subset of all pilots. That question might be better answered on e.g. the Workplace or Legal sites, since it has more to do with legal treatment of disabilities than flying.

It will first and foremost depend on the carrier you are working for and if they have anything in place for such a case. There are personal insurance policies out there to cover this exact case, like this one and this one. Some carriers may offer policies like this in house for their employees as well.
If available to you it might be possible to spend some time in the sim without a medical or (if you are allowed to) instruct and work with other pilots at the company for ground based instruction.

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text:
How can a modified ramjet produce static thrust without a turbine?
A big selling point of the ramjet is its absence of moving parts (hence why it can be translated as "statojet" from other languages). However, an even bigger drawback is that a ramjet cannot produce static thrust, thus a ramjet-powered aircraft cannot take off by itself.
The early Leduc 0.22 and Griffon prototypes solved this by adding a coaxial turbojet. This was further refined with the Pratt & Whitney J58 turboramjet that powered the SR-71 Blackbird.
The problem is that by solving the no-static-thrust drawback, adding a turbojet negates the no-moving-parts selling point.
There are missiles that use solid fuel rockets to solve the problem, using the exhaust of the rocket to compress the air in the ramjet, which is sometimes referred as a ramrocket. However, there doesn't seem to be aircraft using this kind of engine, and missile engines have quite different constraints.
Is there an aircraft engine, working or theoretical, that works as a ramjet in cruise mode, can take off on its own power (without requiring ground installations or a detachable first stage/mothership), and doesn't have the many complicated moving parts of a turboramjet? What are its expected characteristics? If not, what are the showstoppers?
And why can't we simply inject some oxidiser (for example WFNA) to produce static thrust?

The problem of injecting oxidizer is that it has to come from somewhere, i.e. you have to carry it around, i.e. you have more fuel weight and less payload available.

@Federico The idea would be to have a small oxidizer tank to help at takeoff and landing (and in case of emergency). The mass penalty would be a trade-off for using ramjet in the first place.

I don't think the rocket exhaust was fed into the engine, the rocket was used to get the whole thing up to speed where the ramjet could start functioning. Or did I misunderstand you?

@zeta-band Both seem to exist: some ramjet missiles are brought up to speed by a rocket first stage, acting like the solid rocket boosters of heavy satellite launchers. Others have a rocket in the front part, or even solid fuel directly inside the ramjet. The MBDA Meteor missile seems to use the latter.

Perhaps interesting to know is that a liquid fuel rocket engine is generally powered by a turbopump, so the no-moving-parts argument doesn't work for liquid fuel powered rockets either.

The ramjet engine works on the principle that air is compressed by ram pressure before being mixed with fuel and ignited, which means that it cannot by definition produce static thrust. A ramrocket, which functions firstly as a rocket motor, and subsequently as a ramjet is possible.

@J.Southworth How feasible would such a ramrocket engine be for an aircraft? How complex would the whole thing end up being?

A good question, the answer to which would be dependent on other questions; what level of efficiency is required? Which propellants and fuels are acceptable from a safety perspective? What turnaround time is acceptable? My feeling about it is that it would probably be better to launch the aircraft using solid fuel rocket boosters which would then be jettisoned, leaving the aircraft to continue under ramjet power.

A liquid fuel ramrocket engine might consist of a rocket engine combined with a ramjet engine in an over and under arrangement with a shared fuel system supplying fuel to the ramjet, and the same fuel as well as an oxidiser to the rocket motor.

The ramrocket motors used in missiles are solid fuel devices which function initially as solid fuel rockets, then the covers over the air intakes are blown off by small explosive charges allowing the motor to function as a ramjet.

@Federico: Also, WFNA is one of the last things you want to be using as an oxidiser - sure, it oxidises the fuel, but it also oxidises essentially everything else that it reaches, as well.

Well the Pratt & Whitney J58 engines which powered the SR-71 worked in a similar fashion, using a bypass system which allows the engine to operate as a ramjet at high speeds and a turbojet engine at lower speeds.
By the very nature of a ramjet, it relies of stagnation pressure at the intake and inlet throat to pressurize the airflow prior to combustion.  It is just not possible to achieve these kinds of stagnation pressures at speeds under Mach 2 or so.  There was an article in Air & Space magazine a while back about two enterprising Canadian teenagers who tried to fashion a homemade ramjet from iron sewer pipes to power a sled.  They couldn’t get the design to work for this reason.
As such, you would unfortunately need another type of engine to accelerate an aircraft to these fast speeds where a ramjet could work.  Turbojets work well for this application.  So do rocket boosters.  Injecting oxidizer would not be very useful here as airflow through the engine is not fast enough to ensure sustained combustion.

Another way to realise a liquid fuel ramrocket engine, in theory, would be to incorporate the rocket motor into the ramjet air intake centerbody. As the aircraft approached ramjet operating speed, the ratio of fuel to oxidiser being fed into the rocket motor would be increased so that some of the fuel would be expelled from the rocket motor and mixed with air before being burnt. Once at full ramjet operating speed, the supply of oxidiser would be cut off, at which point the engine would be functioning as a ramjet.
Ram jet fuel is basically similar to aviation turbine fuel, but with a slightly higher specific gravity, higher viscosity and lower flash point to suit typical ramjet operating conditions. Concentrated hydrogen peroxide would be one potential oxidiser.

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text:
What is the arrangement of flapping, drag, and feathering hinges on a fully-articulated rotor hub?
Every diagram I have seen puts the flapping hinge closest to the rotor hub, but there seems to be variation whether the feathering comes next followed by the drag/lead-lag, or vice versa.
For this CH-47D the feathering hinge (labeled 'pitch change') is closer to the flapping hinge, followed by the drag hinge (lead lag). The consequence of this is that the lead-lag isn't restricted to the plane of rotation, but changes depending upon how the blade is feathered.

For this hub on the other hand, the drag hinge appears closer to the flapping hinge, with the feathering occurring further away from the hub. This restricts lead-lag to the plane of rotation, but the consequence is that lead-lag could slightly offset the effect of the control rods.

Is there a reason that a particular helicopter uses one or the other arrangement? Is one considered "better" or more the standard option?


text:
Is there an FAA-published handbook for Aviation Physiology?
The FAA has many handbooks, but I don't see one in the list dealing with aeromedical or physiology information.  Does such a handbook or advisory circular exist, or is this information only available within other handbooks such as the PHAK?

Not aware of a handbook, but they do have a GUIDE FOR AVIATION MEDICAL EXAMINERS  https://www.faa.gov/about/office_org/headquarters_offices/avs/offices/aam/ame/guide/media/guide.pdf

I found this Introduction to Aviation Physiology on the FAA web site.

Hey, that's fantastic!  Where in the site navigation did you find it?  It's not in the handbooks section.

I just Google'd for "Faa handbook aviation physiology." Glad it helped.

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text:
Is there any way to relieve the Pilot in Command?
Is there any way to relieve the Pilot in Command besides hijacking and incapacitation?
This question comes from a comment by rackandboneman, who says:

And whose authority is sufficient to make an active pilot in command a pilot out of command?

I gave a joking response, but it got me thinking: are there any ways to remove a PIC from command without that PIC's consent other than hijacking or incapacation, either in the United States or worldwide?

For cause or not for cause? I remember at least one instance that the pilot was acting strangely and the copilot locked him out of the cockpit.

@RonBeyer - Either, but the situation you describe is the kind of thing I was thinking about.

@ymb1 - By involuntarily I mean without that person's consent. Forcible assumption of command is certainly involuntary, but (who knows) maybe Switzerland has a procedure where the captain, FO, and FE all vote, and if it's two to one against the captain, she or he is relieved of command.

@SteveV. If it's Switzerland, wouldn't that rather be something like a 2/3 majority vote among everyone on board, including passengers?

Ae, being from Switzerland I think 500 passengers are likely to decide surprisingly correctly, but the time required to present the situation from all involved sides, in detail, and then build the consensus is difficult to achieve without aerial refuelling.

I guess the swiss would want votes from any swiss citizen residing or visiting in overflown areas, too?

@RonBeyer That seems to be a subscriber-only article.

@JBentley The Internet Archive has a working copy.

There was a case in 2012, where the captain started acting erratically on the flight deck. The first officer tricked him out of the cockpit and shut the door behind him. Passengers restrained the captain until an emergency landing could be made.

In a more recent similar case, a captain was removed before the flight had started because she demonstrated to the whole cabin that she was mentally unfit to fly.

Tricking somebody into lockout is a form of incapacitation, and an action rather than an authority?

Seems that this has happened multiple times if there is something wrong with the Captains behaviour. If he is doing something that clearly endangers the flight, the remaining crew will at least attempt remove him from duty before its too late, regardless if there are rules defined for that or not. Japan Airlines Flight 350 can be an example. If the reasons of removal are obvious, this action is unlikely to be questioned later.

The short answer is no. Otherwise it's mutiny. That said it's exceptionally rare where one has to take control from the Captain, but not so much the Captain taking over from the F/O. The F/O is second in command of a ship. As such has a moral and legal responsibility to his Captain and to his charges. (F/A and pax). If, the Captain is unable to carry out his duties, the F/O must relieve him. On a sea faring ships only the Medical Officer could do this.


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How can the X-59 fly faster than the speed of sound without producing sonic booms?
Lately, NASA and Lockheed Martin revealed the X-59 which looks amazing. I read this article from NASA which already gives some insights of the X-59. The article claims that it will fly faster than the speed of sound without producing sonic booms like here:

NASA’s X-59 Quiet SuperSonic Technology X-plane is designed to fly
faster than the speed of sound without producing sonic booms – loud,
startling noises which can be disruptive to humans and animals.

I was wondering if anyone could explain in some way how this is even possible. I can imagine it must have a specific design, but maybe anyone could explain how this works? Then I'm really curious if this will also happen to fighter jets, since it may be nice advantage to be quite in the sky, right?

Answer to the title, in short, it doesn't. The plane flies a little slower than the Concorde and still makes a sonic boom, just that they've managed to make it much quieter. You cannot eliminate a sonic shock wave. That is just pure and simple physics. You can only attempt to minimize the shock wave, by design of the airplane's parts that make the shock waves happen. The long pointy nose, sharp-edged high sweepback wings, no protrusions, etc. Some experimental designs try to direct most of the wave upwards, but there will still be an audible sonic "thump" as they call it


text:
Is it possible to fly with lower than 1 g-force?
I was watching this video GOING SUPERSONIC with U.S. Air Force Thunderbirds! and at some point (video 15:20 minute) the g-force appear to be 0.7. Here image from the video:

As you can see the g-force is 0.7 very shortly. So I was wondering what this means and if is it possible to have a lower g-force of 1 on earth?

"is it possible to have a lower g-force of 1 on earth?" Yes, it is definitely possible: here you can experience by yourself a 0G and here even some negative G :)

Try a diving board.

Ballistic flight, (which is not aviation unless you consider human cannon balls aviators) is flight with zero g.  Never forget it's the wings that are keeping your butt in the seat. not gravity.

"That's not flying. That's falling, with style"

In the same way that if you ride an elevator or lift downwards as it starts to descend you experience a lighter than normal feeling, you are accelerating downwards so experience less than one G. For aircraft the range of vertical motion is larger so you can have quite long periods of reduced or even zero G - Video. For more severe maneuvers it is even possible to get negative G.
So a fighter getting 0.7G would have been quite normal maneuvering, a start of descent or even simply leveling off from an ascent. Passenger aircraft are perfectly capable of 0.7 G (see links above) but generally avoid it to reduce passenger discomfort..

Another fun example is https://youtu.be/LWGJA9i18Co :)

"G-force" refers to the apparent inertial force that is "felt" by the pilot and the other contents in an aircraft as it accelerates.  For example, if an aircraft is accelerating upwards at the start of a loop, the pilot "feels" an apparent force pulling him downwards into his seat more strongly than usual.
So G-force describes the mirror-image of the force exerted on the contents of an aircraft by the aircraft due to the acceleration of that aircraft.
For a force to be "felt" by the pilot, the aircraft must "push" against the pilot's body, creating stresses and strains within the pilot's body.  The ultimate origin of these forces that the pilot "feels" is the aerodynamic forces created by the wings and other surfaces of the aircraft, and the thrust force created by the motor.  These forces are transmitted as stresses and strains through the structure of the aircraft to the pilot's seat, seat belts, etc and then are transmitted as stresses and strains to the pilot's body, as well as to all the other contents of the aircraft.
In other words, the G-force applied to an object within in aircraft as an aircraft maneuvers could be said to be equal to the net vector sum of all the aerodynamic and thrust forces created by the aircraft, divided by the ratio of the mass (or weight) of the object in question to the total gross mass (or weight) of the aircraft.  Visualized this way, the units of G-force would be Newtons in the metric system, and pounds-force in the English system.
Normally however we talk about G-force by referring to the acceleration that would result from that force, but rather than using the usual units of acceleration, we use the units "G's", where 1 G is the acceleration caused by earth's gravity on an unrestrained object in a vacuum near the surface of the earth.  Expressed this way, the so-called "G-force" (which really would more properly be called "G-acceleration") is equal to the net vector sum of all the aerodynamic and thrust forces created by the aircraft, divided by the ratio of the mass (or weight) of the object in question to the total gross mass (or weight) of the aircraft, divided by the weight of the object in question.
Note the intimate relationship between the G-force or G-acceleration, and the actual aerodynamic and thrust forces generated by the aircraft.  (This is why we use a G-meter to avoid generating too much lift and pulling the wings off an aircraft during aerobatic maneuvering!)  If the pull of the earth's gravity vanished, but the actual aerodynamic and thrust forces generated by the aircraft somehow stayed exactly the same, the G-force or G-acceleration would also stay exactly the same.  (The trajectory of the aircraft, of course, would change.)  So in this sense, the G-force or G-acceleration actually has nothing to do with the pull of the earth's gravity.
Another way to understand G-force or G-acceleration is to realize that the G-force or G-acceleration is the mirror-image of the "felt" component of the actual net force acting on an object or the net acceleration experienced by an object.  Gravity can't be felt, because the force of gravity exerts an equal pull (per unit mass) on every molecule of an aircraft and contents, and so works from "within" to accelerate the aircraft and all the contents as a single entity without creating any stresses and strains within the aircraft and its contents.  So the acceleration component resulting from gravity is not "felt" by a pilot's nervous system, and does not deflect a G-meter, scale, or other similar instrument.
A few examples make these concepts more clear:

An imaginary aircraft in freefall in a vaccuum.  Actual acceleration is 1 G downward, but "felt" acceleration is zero.  Pilot and passengers float weightless.  Note that there are no aerodynamic or thrust forces, so the vector sum of the aerodynamic and thrust forces is zero.  G-acceleration (normally called "G-loading") is said to be 0 G.

"Vomit comet" aircraft in 0-G trajectory.  The wing is unloaded to the zero-lift angle-of-attack, and engine thrust is modulated so that it is always exactly equal to drag.  So the vector sum of the aerodynamic and thrust forces is zero throughout the maneuver.  Pilot and passengers float weightless.  Note that while the "felt" acceleration is zero, and the G-loading is said to be 0G, the actual acceleration is 1-G downward.  The aircraft is accelerating straight toward the earth down at 9.8 meters per second per second throughout the maneuver.

Spacecraft beyond atmosphere.  There is no aerodynamic force.  Whenever the motor is not firing, the vector sum of aerodynamic and thrust force is zero, so the occupants experience zero-G or "weightlessness", regardless of the actual trajectory of the aircraft, i.e. regardless of the actual strength of the gravitational field around the spacecraft.

Aircraft in straight-and-level flight, at a constant airspeed.  Thrust and drag are equal and opposite.  The net acceleration is zero.  Gravity is creating a 1-G downward acceleration component which is "unfelt", while the lift from the wings is creating a 1-G upward acceleration component which is "felt".  The G-acceleration or G-loading is the mirror-image of the "felt" component of the net acceleration, so the G-loading is said to be 1-G downwards.

Aircraft at rest on the ground.  The net acceleration is zero.  There is no aerodynamic or thrust force, but the earth is pushing up against the wheels of the plane with a force that would create a 1-G upwards acceleration if unopposed.  Just like aerodynamic or thrust forces, this force creates stresses and strains that are transmitted through the aircraft structure to the pilot's body.  The "felt" acceleration is 1-G upwards, so the G-loading-- the mirror-image of this "felt" acceleration-- is said to be 1 G downwards.

To experience a reduced G-loading in flight, all you have to do is firmly push the control stick or yoke forward to reduce the angle-of-attack of the wing.  This reduces the lift force, and thus the G-loading.  As the flight path curves earthward, the airspeed will rise, so you'll have to keep pushing the stick or yoke further forward to further reduce the angle-attack if you want to keep the G-loading low.  Sooner or later the process will become unsustainable as the aircraft approaches Vne-- sooner if you start from level flight, and later if you start from a steep climb-- but until that point, you'll get to experience a reduced G-loading.  The seat will push up against your body with less force than in normal straight-and-level flight.

Slightly tongue in cheek, the pilot could experience -1g indefinitely in inverted flight.  Note: indefinite inverted attitude not available in all aircraft.

@WayneConrad -- true enough--

The "G" force (an acceleration), is just the Lift (a force), generated by the wings, divided by the mass of the aircraft. It is a simple formula, F=ma, originally came from Issac Newton and his laws of motion. With a bit of sleight of hand, it become a = F/m.


text:
What were the J47's turbine blades made of?
What materials were used to make the General Electric J47 turbine blades in the 1960's?

It's very likely the J47 turbine blades used wrought iron, with alloying elements of aluminium and titanium. The General Electric J47 turbojet is a very very old design - it first flew in May 1948, only 11 years after Frank Whittle's first prototype gas turbine ran. It was the first axial-flow turbojet approved for commercial use in the United States, and was used in many types of aircraft. More than 30,000 were manufactured before production ceased in 1956.
This 1970 report gives a good summary of the materials used in early gas turbine engines.
It states that early turbine blade materials were either iron, nickel, or cobalt based alloy, both cast and forged. (i.e., there we're a mixture of materials, but the largest percentage of any one material was either one of those three).
Nickel based alloys are the ones that are mentioned the most. They are predominantly used today, and there are quite a lot of them (see table 5 in the 1970 report). But, the J47 is so old, it most probably only used an iron based alloy. This comprehensive report covering material development says, in the section on turbine blades:

....steadily increasing operating-temperature requirements for the aircraft engines resulted in development of wrought alloys with increasing levels of aluminum plus titanium. [But] component forgeability problems led to this direction of development not going beyond a certain extent. The composition of the wrought alloys became restricted by the hot workability requirements. This situation led to the development of cast nickel-base alloys.

So, Ni alloys were not used in very early engines. From above then, it is very likely the J47 used a wrought iron alloy, mixed with aluminium and titanium. This is also supported by Fig 1 from the Rolls Royce document mentioned below (the PDF download is free), which shows only wrought alloys used from 1940 to 1955:

A similar figure, from the TBC report mentioned below, shows Ni based "superalloys" have been used since at least the mid 60's (which is a decade after the J47 production ended!).

While the main constituent of the material hasn't changed since then what has changed is the method of manufacture, from wrought and forged with no crystal or grain orientation, to cast with crystals orientated along the axis of the blade (i.e. hub to tip, called uniaxial), to blades with single crystals. Also, air cooling now exits, with internal passages, and holes on the blade to provide a thin film of cooling air over its surface. The blades also have a thermal barrier coating, that is a ceramic material which basically insulates them from the hot gasses. Originally TBCs were used to gain extra life compared to the life required in the design specifications (i.e. the TBC wasn't necessary to met the base life requirement, but helped give more life). Now days the gases are so hot in some engines, the TBC is necessary just to meet the design specification minimum life. In this case, the TBC is known as prime reliant. See this article for detailed discussion of TBCs.
This article gives a very good summary of the development of turbine blade cooling technologies by Rolls Royce.

J47-25 turbine blades were made of S-816 Cobalt Alloy, which performs better than steel alloys at temperatures as high as 1600°F (1144K), roughly the Inlet Turbine temperature. Remember that this engine didn't have any sort of blade cooling, only the turbine disk was cooled.  You can read more in this NACA report from 1956: https://ntrs.nasa.gov/citations/19930089188


text:
How many aircraft types are cabin crew qualified for?
I always wonder, how many types of aircrafts can a cabin crewmember be qualified for? is there a limitation by say IATA, FAA or EASA?

There shouldn't be any limitation regulation wise, as long as they are up to date with training, licenses, and any other requirements.

@RonBeyer actually in a recent a flight one told me they have limitations, but didn't have the time to ask for more details..

I would guess any limitation might be imposed based on the contract or individual operating entities within an airline.

I know very little about this, but in the US the regulations appear to say that cabin crew must be qualified by aircraft type and the details are part of the approved training program for each operator (airline).
In the US, 14 CFR Part 121 governs airline operations, and 121.392 says:

(a) Any person identified by the certificate holder as a flight
  attendant on an aircraft in operations under this part must be trained
  and qualified in accordance with subparts N and O of this part.

Subparts N and O are far too long to quote here (you can always read them yourself), but 121.421 is probably the most relevant regulation to what you're asking:

§121.421   Flight attendants: Initial and transition ground training.
(a) Initial and transition ground training for flight attendants must
  include instruction in at least the following:
(1) General subjects—
(i) The authority of the pilot in command;
(ii) Passenger handling, including the procedures to be followed in
  the case of deranged persons or other persons whose conduct might
  jeopardize safety; and
(iii) Approved crew resource management initial training.
(2) For each airplane type—
(i) A general description of the airplane emphasizing physical
  characteristics that may have a bearing on ditching, evacuation, and
  inflight emergency procedures and on other related duties;
(ii) The use of both the public address system and the means of
  communicating with other flight crewmembers, including emergency means
  in the case of attempted hijacking or other unusual situations; and
(iii) Proper use of electrical galley equipment and the controls for
  cabin heat and ventilation.
(b) Initial and transition ground training for flight attendants must
  include a competence check to determine ability to perform assigned
  duties and responsibilities.
[...]

I couldn't see any limitation on the number of "airplane types" that a flight attendant can be qualified in, but the training is administered by the airline so if there is a limitation it may set by them rather than by the FAA. 121.427 requires recurrent training (but it doesn't say how often) and I assume that at some point a flight attendant who's qualified on multiple aircraft types could end up spending more time training than actually working on flights. That's unlikely to be something that the airline wants to happen.


text:
Why are TFRs issued around stadiums during games in the U.S.?
I want to know the FAA's reasoning behind issuing TFRs whenever a game is going on in a stadium. Is it just because of a large crowd of people? Do engine noises just bother people? Could an aircraft's wake blow a ball off course?

Security theater.

The 'stadium TFRs' were originally required by Congress after 9/11 to reassure people and encourage them to continue their normal activities without worrying about aircraft flying low overhead. And since then, Congress has repeatedly voted to maintain them; the FAA is just implementing them as directed.
There's more information in FAA Notice 8900.370:

Following the events of September 11, 2001, Congress enacted
  legislation that restricted civil aircraft operations over sporting
  events such as NASCAR, Major League Baseball (MLB), the National
  Football League (NFL), National Collegiate Athletic Association (NCAA)
  Division I Football, and other open-air events containing more than
  30,000 people. These restrictions are implemented via a TFR. In 2004,
  Public Law (PL) 108-199, Consolidated Appropriations Act, Section 521
  was modified to allow civil aircraft limited use of designated
  sporting event TFR airspace.

The TFRs are generally very unpopular with pilots and perhaps as a result, there have always been rumours about other reasons why they were created, or - even if you accept the original reasons - why Congress insists on maintaining them today. For example, the NFL benefits from not having 'unauthorized' aircraft taking pictures or towing banners over their games, when they could be selling those rights exclusively for a lot of money. So perhaps the NFL has pressured Congress to maintain the TFRs for 'security' reasons, while the real motive is making more money. The same comments and thinking are often applied to the 'Disney TFRs', by the way.
Having said all that, there are some arguments that 'security theater' - i.e. feel-good measures that provide no actual security - can have a positive impact on people's comfort and confidence, so it's not a black and white issue. But that whole topic belongs on another site.

From Sporting Event Temporary Flight Restriction:

All aircraft operations; including parachute jumping, unmanned aircraft and remote controlled aircraft, are prohibited within a 3NMR up to and including 3000ft AGL of any stadium having a seating capacity of 30,000 or more people ...

The 30,000 number indicates that the purpose of the TFR is related to the size of the gathering of people. The FAA doesn't issue TFRs for noise like that, and aircraft wake is not going to affect a sports ball in any meaningful way.
There are exceptions to the TFR for flights with specific purposes, or for any other flight that successfully obtains a waiver.

Ah, so it's the crowd. Why only stadiums, then?

I saw at least two banner tow airplanes in the sky over the Daytona 500 on 2/17 while they interviewed drivers before the race. Not when the TFR was in effect for that event.


text:
Do Airbus aircraft fitted with ACT have additional fuel system controls?
Do Airbus aircraft fitted with ACT (Additional Center Tank) have a push button that controls the fuel transfer to the main center tank? If yes, where is it located?


text:
Where is the APU fuel pump on the A320?
I'm looking for APU fuel pump location for A320 aircraft series. I'll be much appreciated if you provide a link to some images, schemes.

According to the image below it seems that the APU fuel pump at the aft side of the center fuel tank.

And this is the view from inside the center fuel tank looking aft:

(instagram.com)
Note the pump still draws fuel from the left line, and not the center tank, it activates automatically if the left side engine fuel pumps don't provide the required pressure.

thank you! Really appreciate it.
I mean the APU has its own fuel pump somewhere on APU assembly.
Or it's only near crossfeed valve? Is there fuel pump on APU under the tail?

@VictorChernobay, there is no point in having a pump in the tail, because that is too high. Liquid pumps are generally pretty bad at pumping gases, so they need to be below the level of the liquid to start—otherwise they'd be full of air and they can't suck the fuel in in such case—which means near the bottom of the tank.

If you are looking for the high pressure fuel pump mounted on the APS3200 accessory gearbox, you can not find a dedicated fuel pump mounting pad in the gearbox. The fuel pump is integral to the fuel control unit and they are mounted piggyback to and driven by the oil pump which is the one that has a mounting pad in the gearbox.

This strikes me as being contradictory to the (unsourced) image in the other answer. Do you have a source (with image if possible) for your information?


text:
Where does the "APU Auto Shutdown" message appear?
I'm trying to find out if and where the "APU Auto Shutdown" message appears on the ECAM.

What specific aircraft?


text:
What are the three sources that are relayed to the brakes and steering control unit of an A320?
There is the sentence:

Electrical signals from the three sources are relayed to the brakes and steering control unit (BSCU) and are computed into the nose steering angle.

The question: What are these sources and where they located?

Where have you extracted this sentence from?


text:
will my pilot's license be considered "Frozen ATPL"?
I am a CPL(A) commercial pilot license holder with MEP and IR ratings.  This CPL(A) has been issued by an ICAO Member State under the rules of Annex 1 to the Chicago Convention.  This country is not a member of EASA and does not operate under the EASA Part FCL rules.
I want to get a job in Kazakhstan, where EASA standards are being actively implemented.  Now for employment in Kazakhstan you need to have "Frozen ATPL".
According to Annex 1 to the Chicago Convention, there is a procedure for a state to give effect to a certificate issued in another state (this process is called validation).  In Kazakhstan, such a procedure exists and has been introduced at the legislative level.  The "Rules for the Recognition of Foreign Licenses" approved in Kazakhstan stipulate that Kazakhstan recognizes licenses if they comply with the standards set forth in Annex 1 to the Chicago Convention, and that if recognized, the license will be equivalent to the Kazakh CPL(A).
It turns out that after going through the recognition (validation) procedure, I will receive a Certificate of recognition of my license and it will be fully equivalent to the Kazakh CPL (A).
Next, I want to prepare and pass 14 ATPL theoretical exams in Kazakhstan and receive a certificate of successful completion.
As a result, I will have such a set of documents:

certificate of recognition of my CPL(A) with qualification marks "MEP" and "IR"
Actually my license is CPL(A) MEP/IR
Certificate of passing 14 ATPL exams

Please tell me, will this set of documents be called "Frozen ATPL" in this case?
THANK YOU FOR FEEDBACK


text:
Delta wing RC aircraft unstable
I've been building and testing an tailed delta wing'd RC aircraft, but it has seemed that the plane is extremely pitch happy and tends to somersault when at high speed, is there some type of easy fix? More counterweight at the back?

Seems most likely you need to move the CG further forward.

How about a picture of it.

pitch happy and tends to somersault when at high speed

The old saw is to move the weight, but the most time honored approach is to glide it unpowered first.  Make weight adjustments here.
This helps sort out stability and trim issues of the design.
Now add power.  Thrust angle must be correct or you wind up with a plane that is very difficult to trim.
I had a similar experience with a Delta Ray RTF model.  If the thrust line was not correct, the plane had to be re-trimmed significantly for low speed landing approach.
You may find that adjusting your thrust angle to push the nose down when power is applied works well.  Models commonly have a thrust down angle of 3 degrees or more.

pitch happy

If you are building an aircraft that will fly through a wide range of speeds, relaxing static stability can help.  Keep in mind that this will no longer be a "trainer", and expertise in piloting will be needed.
This is accomplished by moving weight back and reducing aerodynamic tail downforce.  Remember, moving weight back reduces longitudinal stability as well, meaning larger horizontal and vertical stabilizers may be required.

The center of gravity is too far back.
What angle do the elevons have when trimmed? Do their trailing edges point up or down? I guess they point down ... let us know more by adding to your question!


text:
Determining Sectional Drag Coefficient Using Propeller Geometry
Im trying to teach myself blade element theory for helicopters and propellers, but im getting quite confused.
Most of the papers and textbooks I read will reach an equation for differential thrust similar to equation 2.2 on this paper. They then define the differential lift, the local lift coefficient, the differential drag, and stop just short of defining the local drag coefficient. Instead, they claim it to be negligible, and disregard it in later equations.
I understand that this local drag coefficient is usually determined experimentally, but is there any way to determine it solely by the geometry of the blade? preferably in an algabreic/closed form solution? I found some conflicting answers from wikipedia
The wiki page for the Oswald efficiency number states that:
$$C_{D}=C_{D0}+\frac{C_{L}^2}{\pi{e_{0}AR}}$$
The wiki page for the Lift to Drag ratio states that:
$$(L/D)_{max}=\frac{1}{2}\sqrt{\frac{\pi\varepsilon{AR}}{C_{D,0}}}$$
This same page also provides another definition? I think these differ based on whether the propeller is moving at subsonic or supersonic speeds, not 100% sure.
$$(L/D)_{max}=\frac{4(M+3)}{M}$$
(and yes, these describe the lift-to-drag ratio and not the local drag coefficient, but given that the local lift coefficient is defined, unless im mistaken you should be able to get the local drag coefficient from these ratios)
Finally, the wiki page for the Zero lift drag coefficient states that:
$$ C_{D}=\frac{550\eta{P}}{\frac{1}{2}\rho_{0}[\sigma{S}(1.47V)^3]}$$
Which of these, if any, are applicable to the case of a helicopter?

None of these are useful for you.  They all pertain to a 3D full aircraft.
Please go back and cite specific equation numbers in the reference you cited.
The airfoil local drag coefficient appears in equation 2.6.  It survives through to equations 2.13 and 2.14.  What more do you want?
If you're looking for a reasonable source of data for that number, you'll want to use 2D airfoil data -- either from a wind tunnel reference like theory of Wing Sections data.  Or from a computation like XFoil or CFD.
Usually, we use lower case $c_l$ and $c_d$ for airfoil coefficients.  In the reference you cited, it appears they use mixed case $C_l$ and $C_d$ for airfoil coefficients -- but we pretty much universally use $C_L$ and $C_D$ for 3D aircraft-level coefficients.

I'm trying to teach myself blade element theory for helicopters and propellers, but I'm getting quite confused.

Advanced aerodynamics is nothing that you can teach yourself unless you have a good understanding of calculus and fluid dynamics or aerodynamics.

They stop just short of defining the local drag coefficient. Instead, they claim it to be negligible, and disregard it in later equations.

You misread the paper. In blade analysis both drag and lift contribute in a substantial way to the thrust and to the torque and the figure 1b in the paper clearly shows it:

Lift $dL$ and drag $dD$ both contribute to thrust $dT$ as given in equation 2.2 and they both contribute to torque $dQ$ as given in equation 2.3. Note that in all of the following developments of those two equations both lift and drag survive, like for example in equation 2.13 and 2.14.

I understand that this local drag coefficient is usually determined experimentally, but is there any way to determine it solely by the geometry of the blade?

The drag coefficient on those equations depends only on the local airfoil. If you don't want to use experimental values you can interpolate the shape of $C_d$ vs. $\alpha$: normally a second order interpolation (parabolic) is enough.

I found some conflicting answers from wikipedia

They are not conflicting, they simply have nothing to do with the blade analysis you are investigating.


text:
What is this aircraft shown in 'Operation Buffalo' (TV show)?
Its registration appears to be VH-AES but a search of the Australian database shows it as being a DC-3??

Please [edit] your question to include the name of the movie.

It looks like a Bristol Type 170 Freighter: (All images are from the linked Wikipedia article).
The more I look at the images you posted the more it looks like a CGI than an actual aircraft.
Regarding the registration:

To me it looks more like VH-AEN
The images you posted seem like they are from a movie. Movies often use fake registration numbers.
Next time it might be beneficial to mention the name of the movie.

It's absolutely a Bristol Freighter, this one is CGI I'm pretty sure as there aren't any flying examples to the best of my knowledge.

That rear 3/4 view reveals this to be one funky lookin' plane! I understand that the design elements make the most of the cargo deck, but still that's a weird looking bird. Also do the loading ramps really extend from the chin without the cargo doors being open? That just adds to the oddness.

Thank-you. My son suggested it was CGI too. The show is a new TV Series on the ABC (Australian Broadcasting Corporation) "Operation Buffalo" set around the Maralinga Atomic Testing grounds during the 1950's. As Bristol were involved with the Rocket project at Woomera (also in South Aust), I guess there's a nice synergy using a Bristol in this show.

I'm not sure if the show is geoblocked, ABC have a VOD (ABC iView). If you liked Australian movies "The Dish" or "The Castle" you may enjoy this one.

It was CGI shot at the HARS Museum at Albion Park NSW.  A temporary green screen was built around a C-47. Aircraft VH-AES, VH-AEA and VH-AEF were used, all the internal and external aircraft footage was shot in and around the DC-3 C-47's at the Museum.

Thanks for the additional info. If you have any links or other sources for the claim, [edit]ing them in will improve your answer.


text:
Estimating the fuel required in terms of flying distance and total weight
I am looking for a mathematical model to estimate trip fuel required. I have searched the internet but not found any specific mathematical model as such. The question is formulated as follows:
Let $W_0$ be the weight of a particular aircraft with a given fixed set of technical specifications (say Boeing 737-800) without any fuel, passenger or cargo, $W_c$ be combined the weight of the passengers, their baggage and all additional cargo and $x$ be the flying distance (take off to touch down).
Question:

What are the best known mathematical models or algorithms to predict or estimate the minimum amount of fuel required $W_{f_{min}}$ in terms of $W_0, W_c$ and $x$ for this aircraft?

Assumptions: For simplicity, let us assume that the following conditions are true

Weather is perfect i.e. no additional fuel required due to bad weather
There is no air traffic due to which additional fuel is burned
The pilot is good and flies tries to minimize fuel consumption
In case any addition information is required or missing, please
assume    them in your answer and proceed.

There is no such formula because the engine efficiency is unknown. E.g. For the same zero-fuel weight and distance, new models of the same family achieve 15% better fuel efficiency.

For the given aircraft, the model is fixed and so its technical specification including the engine efficiency is fixed. But we can do even better. Since engine efficiency is expected to decrease with time,  for a particular aircraft's using its data, engine efficiency can be tracked as a time series to I don't see why this should be considered unknown.

The best know algorithm is the Breguet equation


text:
How to find if an aircraft is inside an airspace using latitude and longitude?
I have the data of latitude and longitude of $n$ points on the boundary of the airspace of a country. I also have the coordinates of the current location of an aircraft. Using this data, how do I find out of the aircraft is inside the airspace or outside.
For the sake of simplicity we can assume the boundaries of the airspace form a convex polygon.

What have you tried to do? This sounds more like a geometry problem (i.e. "is this point inside this area?") than an aviation one.

I am still trying to solve it. All aviation engineering problems are eventually physics and mathematics problems so I don't see and issue with. As far as this is concerned this is a very common question so I am sure current airlines have some methods to answer this? I am looking for that method.

Such low level problem solving might not be public knowledge, if they have developed their own algorithms, but you can always ask for general purpose algorithms on math.se. Here, it depends if people are interested in it. Still, it is missing what have you tried and why you cannot find the answer.

My trying is still in progress and I hope to crack it but then don't have to wait until I finish my trying to ask a question. Why reinvent the wheel if it is already invented. It is a  mathematically tough problem for that reason you don't see too many solutions in the internet which can both mathematically accurate and practically implementable.

If you don't get a good answer here, you might also try gis.SE. And depending on exactly what you mean by "airspace", you might have to consider the aircraft's altitude too.

First step is to take the min/max of all the Lats/Longs to get 4 points, a square. If the point is inside this, then keep going, if not exit. After that, it isn't any different than other problems like this one. If you want to get really fancy, convert the points to ECEF from lat/long so that you take in the curvature of the earth into account.

@RonBeyer should you post that as an answer? (and personally I would not suggest ECEF to consider Earth's curvature, since ECEF does not do that really well)

It is just a well-known computational geometry problem called PIP (point-in-polygon). I assume that the airspace is pretty small, and we can consider its boundaries as lines (not curves) in a plane.
Firstly convert latitude and longitude minutes and seconds to fractions. Then use any of PIP algorithms (or libraries, if you do it in any programming language).
For more information check: wiki or this link.
You can also use WolframAlpha for that, or any programming language with a specific library (for example, OpenCV does it very well in C++ or python).


text:
What airfoil design does the MQ-9 Reaper UAV use?
What airfoil design does the MQ-9 Reaper UAV use?  Alternatively, what similar airfoil designs exist?
I'm running simulations for the effects of vortex generators for a school project and I would like to study the Reaper drones.

I'd suggest using gliders as they have a lot more published data, and even vortex generator studies in the open literature. Military aircraft and UAV's do not generally have data for the public eyes. If it's a school project, you'll be at safer grounds in publishing your results too.

Use the GA(W)-1 as a replacement. It should not be too different and a lot of work on it has been published.

GA(W)-1 by no means at all close to GW series airfoils. GW series in intended to fly ~1-0.5 Million RN while GA(W) is intended to fly ~10 million. And operating CL range is also very different.

The wing root of the General Atomics RQ-9 is the Drela GW-19/GW-25.
The wing tip airfoil is the Drela GW-27.
Because of their application, you will likely have difficulty finding study results of vortex generators used on that blended airfoil. There are papers, but I have only seen them in the DTIC library, and I do not recall the classification of them. However, the aircraft has been exported, so you may find some open literature on the airfoil, and the adaptations and optimization of it.

Sorry to resurrect such an old answer but do you remember where you got this information?

Similar airfoil if you go higher Reynolds number is NLF 1015 and NASA LRN 1015.
One paper specifically investigated what you have suggested above is this.
AIAA-2003-0211
Enhanced Airfoil Design Incorporating Boundary Layer Mixing Devices
Michael Kerho and Brian Kramer
On the original airfoil design without vortex generators.
THE DESIGN. OF AN AIRFOIL. FOR. A HIGH-ALTITUDE,. LONG-ENDURANCE. REMOTELY. PILOTED. VEHICLE. N9 0- 12 545. Mark. D. Maughmer.


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Would a Cessna 172 be as safe as an airliner if flown by an airline pilot?
I know that general-aviation flight is much more dangerous than airline flight. Is this because of the planes or the pilots? If an airline pilot is flying a Cessna 172, is that Cessna as safe as an airliner?

One of the certification requirements for an airliner is that it must be able to suffer an engine failure at V1 with maximum takeoff weight and still safely take off, establish a positive rate of climb and clear an obstacle with one engine out. How's your Cessna 172 comparing to that?

The post is not asking for a comparison of risk of airliners vs 172s. It's asking if there's any safety benefit of having an extremely overqualified pilot on board. I'm saying the benefit is negligible. When you filter out crashes from overweight takeoffs, incompetent maintenance or preparation, and weather, good pilot on a sunny day with enough gas, you end up with something that's really not very dangerous.

There's a lot of levels of skill and experience in "airline pilot". A 747 pilot who hasn't flown a small single-engine plane in 25 years is very likely to be dangerous in one. A pilot who flies C208s for FedEx every day is going to be far better.

We have to be really careful about selection-bias comparisons because they almost always mislead us to false conclusions.  If we cherry pick one guy who died wearing a seat belt, and one guy who survived not wearing one, we can prove seat belts don’t work.  But over a larger sample size we’d be profoundly wrong.  If I could hand-pick the best 172 pilot I know, would I choose them to fly with me on my top-secret, highs-risk 172 mission?  Yes.  If I had to wear a blindfold and randomly choose any 172 pilot and any ATP, as long as they had a recent 172 checkout, I would choose the latter.

There’s no doubt that the majority of general aviation accidents can be attributed to some human element and are not simply an unexpected failure of a system component.
But there’s several reasons I would suggest that there’s still a greater risk.

Redundancy of systems and robustness of systems in an airliner more than offsets the risk of the systems complexity the airliner brings.

Turbine engines are more reliable than piston engines.  A large jet engine can take $10 billion to develop over a 10-15 year period, and easily cost millions or tens of millions each, so jet engines aren’t exactly fighting fair with pistons, LOL.

Speaking of engines, there’s always more than one of them on an airliner.

Systems like anti-icing are quite common on an airliner and rare on 172-class airplanes.

An airliner is crewed, and I don’t just mean in the air.  The dispatchers are part of the crew.  The operations center is part of the crew.  Systems specialists, weather specialists, etc. are all part of the system.  At an airline, How many people are involved in making the wether go/no-go decision?  It’s not one.  How many people are involved in getting and verifying the right amount and quality of fuel got loaded onto the airplane?  It’s not one.

Engine analysis in a modern jet is absurd.  The airline, and the engine manufacturer, receive telemetric data in real time about the performance of the engine, so any temperature anomaly or vibration is reported.

An airliner is well equipped from an excess power and ceiling perspective to move quickly through or out of adverse conditions like icing or avoid weather.  A 172 flies through an atmosphere that airliners only pass through momentarily.

Speaking of the airspace used, many airliners will spend almost their entire life in radar coverage flying on an IFR flight plan.

The systems automation in a typical airliner of today means that a flight control computer, an engine control computer, and augmented stability systems sit between the pilot’s input’s and the airplane itself.  For instance, an airliner may have engineered into its flight controls the ability to manage a critical-engine-out throttle and rudder inputs, where a light twin pilot has to manage all that themselves.

We could keep going.  With a whiteboard and a few minutes we could brainstorm our way to another 5, 10, or 20 factors that tend to make airliners safer than GA aircraft.
But to me, it really comes down to how every decision is managed by multiple people (some not even on the plane) through the lens of a rigorous, disciplined process, supported by robust systems.

This is a very good answer, but the question asks about the benefits of a better pilot, not of a better machine

@sophit It does answer my question. It could be summarized as "No, a Cessna 172 flown by an airline pilot is not as safe as an airliner flown by the same pilot." The rest is just listing reasons why.

@Sophit, actually not.  If you read the question, it is about whether the improved safety record of airlines transfers with the pilot, or whether there are other ingredients besides the pilot’s experience.

@Someone: ok. It would have been anyway interesting to know if a professional pilot had reacted in a different way in respect to a Cessna pilot to the same machine problem. For example: would a professional pilot foresee an icing problem? Would a professional pilot react differently to an OEI case? And so on. I know for sure that the other way around applied in the past, where (apparently) jetliner pilots were helped by their glider skills to better manage an incident. Anyway both +1

They receive engine data in real time? Do you have a citation for that? Makes one wonder if the MH370 engine data was being sent on real time.

@tedder42 Back at the time, the Rolls Royce engine messages sent over ACARS were a big deal in the news.  But after more analysis it appeared the ACARS system was manually switched off, which led to increased speculation of an intentional act.  Since MH370, the frequency of ACARS messages has been increased, and can now be transmitted over a wider array of satellite services.  Forbes has written quite a bit about it.  https://www.forbes.com/sites/johngoglia/2014/03/13/aircraft-engine-monitoring-how-it-works-and-how-it-could-help-malaysia-air-370-crash-investigtors/?sh=595611497620

@MaxR I forgot the data was from the engine!


text:
Is an autopilot failure an emergency?
If the autopilot of an airliner fails, but everything else still works, weather conditions are good, and the pilots are able to hand-fly the plane with no problems, is this an emergency? Would they divert to the nearest suitable airport, or continue to the destination?

It's not an emergency, but there is a significant workload increase because both pilots now have to be paying attention full time, with one watching the other flying, vs only one (watching the AP) when the AP is engaged, and the other doing paperwork, or napping (sometimes).  But otherwise, not that big a deal.
Lots of airplanes only have a single autopilot system (following commands from one of two Flight Directors). You need a working autopilot to fly above 29000 ft in RVSM airspace (where crossing traffic is only 1000ft above or below), but you don't necessarily have to have it engaged, and ATC doesn't know whether you have it engaged or not. Lots of pilots will hand fly for part of the cruise phase just for something to do, paying very close attention to the altitude to avoid getting busted for a deviation.
In any case, if the autopilot actually fails, you are no longer RVSM compliant and are required to notify ATC of the failure, and you will likely be told to descend below RVSM airspace, to finish your trip (which can impose a significant fuel burn penalty on a turbofan or turbojet).  At that point you just carry on, and may decide to alternate hand flying back and forth every 15 minutes, or whatever, to limit workload on each pilot.
Lots of small commuter airplanes, like Beech 1900s, are not equipped with autopilots at all (if the airline is cheap) and the crews just alternate hand flying all the time (they can't get get up to RVSM airspace if they wanted to, so that's not an issue).

Nice answer. Many GA pilots don't realize holding course, attitude and altitude by hand is harder at (say) 35,000 feet and Mach 0.82 than keeping a Cessna 172 going at 6,000 feet. So the workload is significant, but as you say not an emergency.

The CRJ200 is so snappy in roll, and the aileron feel units, W cams built into the quadrants back at the rear spar, have a high breakout force, so when you apply a bit of wheel to bring up a wing while in fast cruise, by the time you break it out of center it's always a bit too much the damn airplane having so much roll power, and you end up making little back and forth corrections trying to get the wings level. Annoying.

Is it true that "Lots of small commuter airplanes, like Beech 1900s, are not equipped with autopilots at all?"  I think that highly unlikely.  New Cessna 172s come with an autopilot.  During the cruise portion of a flight, maintaining the assigned altitude would probably be done with fewer and smaller corrections by an autopilot than a human, making it more economical to have an autopilot.  Autopilots can reduce workload, improving safety, even a cheap airline would want that.

Oh yes.  I know a couple of ex 1900 drivers that worked for a small line that didn't have APs in their fleet.

@JohnK OK, I believe you.

I have hand-flown an airliner both sectors (there and back) on one occasion. It was 2 hours there and 2 hours back (dispatched with the autopilot inoperative) so in good weather it is not an issue. But as pointed out in another answer, it is very demanding. It is difficult to hand fly at 35,000 feet with cabin crew with meal carts and passengers walking back and forth - not an ideal situation. It would be prohibited in RVSM airspace however.
Not part of the question but included for a complete answer: check in the Minimum Equipment list and/or Dispatch Deviation guide for the airplane. Some airplanes are certified to fly single crew in IMC; a functional 3 axis autopilot might be a prerequisite. If it fails in flight in IMC it might be construed as an emergency. In the image below, the airliner does not require an autopilot for dispatch if weather and operational requirements permit, therefore it would not be an emergency if it failed in flight under those conditions.

Regarding the last paragraph, I'm not sure it's a function of the airplane as much as the operating certificate.  I flew part time for a 135 carrier that was certified for single pilot operations, and one of the conditions was having an operative autopilot during IMC.  It wasn't required per the MEL, so it could be overcome with a First Officer in the right seat.

As an aside: There is at least one instance where an autopilot failure or unintended disconnect is an emergency: when you fly a plane into icing conditions on autopilot, and the autopilot progressively trims the plane to maintain the programmed altitude profile as it ices up, right up to the point where it runs out of trim authority and then kicks off-line, handing the pilot an unflyable plane which then immediately spin/stalls into the ground.

Is there any way to recover from this scenario?

@Someone If ice has already built up to the point that the autopilot disconnects, you are in a very, very bad position. All you can do is fly the airplane as best you can- get out of icing conditions and land as soon as possible. Unless your POH says otherwise, keep the airspeed up (but below Vne!) and avoid configuration changes- the airplane is still flying, if barely, and you don't want to change that.

Sounds like the autopilot doing what it's designed to do, rather than failing.  The cause of the accident is the icing, not any failure of the autopilot.

Yes, it's really more like the autopilot shutting off is revealing an emergency you just haven't noticed up to that point.

@RalphJ: Safety would be improved if the autopilot said "no" long before reaching its control authority limits on the basis of "level flight does not need this much pull up". The autopilot failing to recognize the abnormal circumstance is a contributory factor.

As an avionics software engineer I would not consider this situation as an emergency. Please see following explanation may give you an insight.
Software Level which is frequently called as the Design Assurance Level (DAL) as defined in ARP4754 and DO-178C, is determined from the safety assessment process and hazard analysis by examining the effects of a failure condition in the system.
The failure conditions are categorized by their effects on the aircraft, crew, and passengers.
Basically the effects are categorized as;
Catastrophic - Failure may cause deaths, usually with loss of the airplane.
Hazardous - Failure has a large negative impact on safety or performance, or reduces the ability of the crew to operate the aircraft due to physical distress or a higher workload, or causes serious or fatal injuries among the passengers.
Major - Failure significantly reduces the safety margin or significantly increases crew workload. May result in passenger discomfort (or even minor injuries).
Minor - Failure slightly reduces the safety margin or slightly increases crew workload. Examples might include causing passenger inconvenience or a routine flight plan change.
No Effect - Failure has no impact on safety, aircraft operation, or crew workload.

Under certain typical conditions loss of Autopilot is not an emergency:

The loss of autopilot is annunciated (like through a chime or flashing indicator)
We're not discussing helicopters where Stability Augmentation is more than a little convenient.
The flight plan doesn't require autopilot.  This would not be the case for RVSM altitudes, a CAT II or CAT III approach, or an approach procedure with RNP < 1 NM, like the approach from the North at Palm Springs.

Under certain conditions like un-annunciated loss of Autopilot, loss of Autopilot might be considered a Major Hazard, in other words something that's likely to cause significant additional workload for the pilot or which considerably reduces the safety margin. For certification aircraft are designed so that Major Hazards occur at less than 10⁻⁷ probability per flight hour (i.e. less than once in the lifetime of a single aircraft, but as much as a few times in the lifetime of a whole fleet).  For more typical flight scenarios annunciated loss of Autopilot functionality might be Minor, that is a slight reduction in safety margins.
A good resource for looking into questions like this is the NASA ASRS database, which returns several dozen reports of autopilot disengaging unexpectedly like ACN 1774748 or ACN 1781223. Although there is reporting bias there - any incident reported is going to be serious enough to file, but not fatal.
This analysis can be a little complicated, and guidelines like the Minimum Equipment List tell pilots what's certified for their aircraft, while standards like ARP4761 provide a framework that designers use to answer questions of "how bad is it if X fails?". Simple questions like "is yaw damper safety critical?" can vary depending on the design of the aircraft.
Keep in mind the term "autopilot" can be confusing. I'm not referring here to a Fly-By-Wire system which is clearly critical. I'm referring here to a system that computes and displays guidance commands, trims the aircraft, and may even command the control surfaces if there is a way for the pilot to override such control surface commands. Loss of some of those sub-functions by themselves, like trim, may not as bad as indicated above.


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What was the first law requiring licensing or certification for pilots?
What was the first law passed by a government (e.g. not a private organization's policy) requiring some kind of licensing or certifications for civilian pilots?

@RTO no particular country

Related: https://aviation.stackexchange.com/questions/99139/was-the-first-us-government-issued-pilot-license-issued-in-1927-or-28/99141#99141

What was the first law requiring licensing or certification for pilots?

Connecticut, a pioneer State for aviation, passed an act on June 8, 1911 to regulate aircraft registration, identification, and pilot licensing: "An Act concerning the Registration, Numbering, and Use of Air Ships, and the Licensing of Operators thereof."
According to connecticuthistory.org:

The Connecticut statute was the world’s first aviation law, and it quickly became the model for similar laws in other states. The law was enforced at first by the Secretary of State, and later by the Commissioner of Motor Vehicles, who for a while doubled as the state’s Commissioner of Aviation.

The full text is available at Connecticut State Library, page 1348 and following:

Other States followed, e.g. in May 1913 the NY Times published this:

This answers the OP though this is not an exam or a certificate. But such certificate were issued as early as 1909/10 by the Fédération Aéronautique Internationale. I don't know if they were required by law nor when. However they were required to participate to airshows and air races under the auspices of the FAI (airshows and races were common in Europe during this era).

Thank you! When was the Connecticut law passed?

@Someone-OnStrike: I updated my answer, the first act was approved on June 8, 1911.


text:
Is "Aviate, Navigate, Communicate" legal in Part 121 operations?
14 CFR § 121.557(c) says in part, (emphasis added)

Whenever a pilot in command... exercises emergency authority, he shall keep the appropriate ATC facility and dispatch centers fully informed of the progress of the flight.

Doesn't this require a pilot to "communicate," even if it distracts from "aviating" and "navigating"? 14 CFR § 121.557(a) allows the PIC to deviate from regulations if necessary, but I'm not sure this applies to 121.557(c)?

121.557(a) is pretty clear:

In an emergency situation that requires immediate decision and action the pilot in command may take any action that he considers necessary under the circumstances. In such a case he may deviate from prescribed operations procedures and methods, weather minimums, and this chapter, to the extent required in the interests of safety.

The pilot in command can deviate from any part of Title 14 Chapter I (in other words, parts 1 through 199) to the extent required in the interests of safety. This includes 121.557(c).

Or... simply do (a) first, then (c).

I've actually done that... not the ATC part, but the dispatch part. We had a medical emergency on board, and went screaming into Atlanta at the speed of heat. Dispatch wanted a phone patch, and I said No Way -- we're plenty busy here, going fast, dodging weather, so call me at the gate, bye.  The dispatcher was cool with that answer via ACARS (it was a supervisor who was pushing for the phone patch), and I never heard anything about it afterwards.


text:
Is there a standard way to identify propeller blades?

Obviously, as Julio pointed out, Chuck's method of identifying propeller blades is ineffective. Is there a standard way to identify blades, other than tautological statements like "There is a dent in the propeller blade with a dent"?

some guy in the comments of that comic wrote,
"Simple. It´s the left blade when the blade is left of the plane when cylinder #1 is at TOC",
I don't know what about turboprops or more than 2 bladed props

Do you need the joke explained?

You have to get a can of Prop Wash and clean off the blades to find the L & R marks.

@MichaelHall no, I get the joke. Calling one blade "left" and the other "right" isn't helpful because the propeller rotates. I'm not asking for an explanation of the joke; I'm asking whether there is an actual right way to name a particular blade.

Well, that plus getting right and left mixed up.  Anyway, there might be a good question in here about whether individual blades on a CSP are serialized for traceability when replaced or overhauled, but fixed pitch props are one piece so there is no need to differentiate, and as the cartoon points out... you can't.

On a constant speed propeller, blades may be numbered as parts of an assembly, although not by markings visible on the outside. On a fixed pitch aluminum club propeller, there are no blade markings.
If you see a big ding on a blade during a walkaround, you are just going describe with without identifying which blade, which will be obvious to the mechanic who goes to dress it out.


text:
How much of the empty mass of a typical airliner consists of rivets?
How much of the dry mass of a typical airliner (let's say a Boeing 737 or Airbus A320, if a particular model is needed) consists of rivets used in assembling the plane?

Could you unaccept my answer? I'm not confident it's correct and like I'd to delete it pending some more research.

@Chris sure, I unaccepted it.

A similar question with a slightly different answer would be the weight caused by the addition of rivets. There is some overlap of material where it is riveted together which adds slightly to the weight compared to using larger non-riveted sections. Partly countering this is the rivets replace a (very) small part of the material. Further complicating that question would be taking into consideration having to use thicker material to make larger sections possible. But still it's interesting to think if you could hypothetically "3D print" a hull, how much less would it weigh than riveted sections

German Karlsruhe Tech managed to build a 4 mm thick wall concrete kart body on a prestressed concrete plate (see Indian concrete magazine), at a density of 2.6 gr/ cc, It isn't bad

$\def\cm{\rm cm}$ I cannot find authoritative answers. But we can do some ballpark estimates. This is an image of an A320 fuselage. Making a lot of assumptions, but one hopes that they will more or less balance out. I would say that separation between rivets is around $1.5\cm$ (using a window height of $36\cm$ to compare). The spars seem to be separated by about $50\cm$, with rivets all around. The fuselage diameter is 395cm, which gives us a circumference of $395\times 3.14 = 1240 \cm$. The length of the fuselage is $3757\cm$, which gives us $3757/50 = 75$ spars. That gives us
$$\tag1
75 \times 1240\cm \times\frac1{1.5\cm} = 62,000
$$
rivets for the spars. There are also seem to be rivets along the fuselage, separated by 15cm. This would give us
$$\tag2
\frac{1240\cm}{15\cm}\times \frac{3757\cm}{1.5\cm}= 207,000.
$$
A crude estimate looking at the windows gives me $200$ rivets per window, with $88$ windows, so
$$\tag3
88\times 200 = 17,600.
$$
I cannot find a good enough picture of the wing, but based on this one I will assume the same rivet density as in the fuselage. The surface are of the fuselage is $1240\cm\times 3757\cm = 4,658,680 \cm^2$, and we estimated (from $(1)$ and $(2)$) $269,000$ rivets, so
$$
\frac{269,000{\rm\ rivets}}{4,658,680\cm^2}= 0.06 \frac{{\rm\ rivets}}{\cm^2}.
$$
The wing area of the A320 is $1,226,000 \cm^2$. Doubling this because we want to also count the underside, we get
$$\tag4
2\times 1,226,000 \cm^2 \times 0.06 \frac{{\rm\ rivets}}{\cm^2} = 70,791 \ \rm rivets.
$$
We are ignoring the other surfaces, but let us assume that the contribution is not that significant. We get a total of $$
(1)+(2)+(3)+(4)= 357,391 \ \rm rivets.
$$
This number looks coherent with sources that mention 3 million rivets for a 747 or A380, which weight around 10 times as much as the A320.
As for the weight of a rivet, this article mentions about $300$ rivets in $0.25\ \rm lbs$ bag. That's
$$
\frac{0.25\ \rm lbs}{300\ \rm rivets}\times \frac{\rm kg}{0.454\rm lbs} = 3.78 \times 10^{-4}\frac{\rm kg}{\rm rivet}.
$$
This gives us a total rivet weight of
$$\tag5
3.78 \times 10^{-4}\frac{\rm kg}{\rm rivet}\times 357,391 \ \rm rivets = 135\rm kg.
$$
The empty weight of an A320 varies according to variants, but one source I found says $42,220\ \rm kg$. This gives the proportion as
$$
\frac{135}{42220} = 0.003,
$$
or $3/1000$.


text:
Would the Wright Flyer be considered ASEL or AMEL?
The Wright Flyer had two propellers driven from one engine. Aside from airworthiness issues, would an ASEL or AMEL rating be needed to fly it?
What about the opposite design, with two engines powering one prop?

Well, it's in the name. Single ENGINE, not single propeller.  It's the number of torque generators that matter, because that's what determines the performance hit if one goes south.
You can have two engines driving one propeller, but if one quits, you are still stuck with 50% power just as if you had two propellers, so it would be considered a multi-engine airplane (though it may get a unique designation as multi-engine-single-propeller for identification purposes).

There have been a few airplane models with 2 engines 1 propeller: Wikipedia list

@jpa there's also a list of pushers!

The Wright Flyer has some failure modes in common with twin-engine aircraft, such as asymmetric thrust if one of the drive chains fails.

Look into the Soloy Dual Pac -- including their C208 conversion.  Also, multi engine helicopters may be relevant.

@RobMcDonald how does the FAA handle pilot training requirements? Is there a special multi-engine sub-rating for that particular STC?

@Mark Ironically, if that happens you're going to have to throttle way back to keep the remaining prop from overspeeding, so you are effectively in the same boat as a regular twin.

@JohnK I'm not sure.  Soloy certainly advertises it as the reliability of a twin with the symmetry of a single (no Vmc).  I doubt you could get your twin engine rating in one (or take your twin engine checkride).  There was a previous question about the Soloy...  https://aviation.stackexchange.com/questions/3271/is-the-soloy-dual-pac-recognised-as-two-engines-or-one-engine


text:
Could leading-edge dynamic stall occur for a tripped airfoil?
As far as I know leading-edge dynamic stall is characterized by the formation of a Leading edge vortex. This leading edge vortex forms due to the 'bursting' of the LSB (Laminar separation bubble). However, if the airfoil is tripped on the upper surface to make the boundary layer fully turbulent, does that suppress the leading edge vortex? if so, what will be the process leading to the dynamic stall in this case?
Your help is greatly appreciated.

if the airfoil is tripped on the upper surface to make the boundary layer fully turbulent, does that suppress the √leading edge vortex?

I would say no, because supercritical wings that have that LSB problem, and so suffer from leading edge stall, aren't improved by leading edge contamination, like frost coatings or heavy bug accumulations, which can be presumed to destroying laminar flow well forward of the normal transition point.
On the CRJ200, which has a particularly nasty unrecoverable LE stall due to LSB formation at the leading edge, contamination only serves to reduce the stalling AOA to below shaker/pusher onset, without making the stall any more benign, as a number of frost contamination crashes have shown.  The bubble is still there even with the rough surface forward of it, and so the wing still lets go all at once, just at 9 degrees instead of 15.
The LSB formation is particularly bad on supercritical wings because the profile has an odd kind of "corner" or discontinuity in the curvature because of the extra thickness forward, which gives a kind of squared off profile at the LE.


text:
Gap between F22 ailerons and flaperons
You can see in the below picture that there's an F22 on approach (I think) and this is almost a perfect bottom view of the plane while it's going straight, it isn't banking.
There's gaps between the ailerons and the outward part of the wing, and gaps between the aileron and the flaperons. I thought sealed ailerons were more effective and and a lower drag as show in this answer about external aileron seals.
Is this much of a visible gap negligible?

Due to the high loads sustainable by this kind of airplanes, the structure tends to deform quite a lot (gif source - that's an A350 but it gives anyway an idea of what I mean):

Having moveable surfaces perfectly "sealed" might simply jam them under load, that's why the gaps that you see in that picture.

Deform horizontally?

Besides the fully valid point of @sophit, it must be noted that the flaps, elevators and ailerons of the F-22, F-35 and B-2 have a pillow edge, which means their sides end in a sharp edge to reduce side emissions of electromagnetic radiation. This makes the gap visible at odd angles where conventional control surfaces with a triangular side would block the light. The gaps themselves are not larger than those of comparable airplanes.

@AadirajAnil Imagine the wings bending up, causing the top edges of the gap to come closer together.

This answer sounds sound, I'll wait for anything else and mark it. I think the information about pillow edges added by @PeterKämpf is also supporting this answer well.


text:
How much of an improvement would a 1% weight decrease on an airplane be to the industry?
Say I thought of a very easy and inexpensive way to reduce the takeoff weight of a commercial airplane (body, fuel and passengers) by 1%. How much would this mean to the industry? Would it make much of a difference, or would the savings be insignificant enough to not really be worth anyone's time?

Comments are not for extended discussion; this conversation has been moved to chat.

There is an easy way to get an idea of what magnitude the savings are: The Breguet equation can answer this. You first calculate a reference aircraft and then start all over with one that weighs 1% less. The difference in fuel consumption shows how much fuel is saved per flight.
Our reference design is the A320 which has an L/D of 18 and we let it fly a trip of R = 2,500,000 m. $m_1$ is take-off mass and $m_2$ landing mass. Allow for 3 t of fuel reserves and plug that into the Breguet equation, using a fuel burn of $b_f$ = 0.000018 kg/Ns and a speed of Mach 0.78, which equates to $v$ = 262 m/s in 11,000 m altitude:
$$m_1 = m_2 \cdot e^{\frac{R\cdot g\cdot b_f}{v\cdot L/D}}$$
The landing mass $m_2$ is the operational empty mass OEW + 18 t payload + 3 t of fuel reserves = 63.6 t. The take-off mass $m_1$ is 10% higher, so the difference in fuel consumption is 1% of that trip fuel of 6,239 kg or 62 kg. That is not much for a single trip.
But now consider that this one A320 will fly 50,000 trips before it retires. Over its lifetime the 1% in mass reduction will save 3,119 metric tons of fuel. This fills 29.4 DOT-111 railway tank cars!
And there are about 12,000 airliners of 150 seats and more and easily twice that number if all regional jets are included, flying 3.8 billion passengers and 53 million tons of freight per year on 35.4 million flights. If we make the heroic assumption that our A320 flight is typical, this translates into global fuel savings of about 2.2 million tons of fuel per year if only 1% of mass could be saved on every airplane.
Another way to approach this is the average fuel efficiency of modern airliners which consume between 3 and 3.5 liters of fuel per 100 passenger kilometers. Using ICAO's number of 6.6 trillion passenger kilometers in 2015, this would equate to 174 million tons of aviation fuel used per year for revenue passenger transport, assuming a mean density of kerosene of 0.81 kg/l. The same source gives an average load factor of 80%, so one fifth of seats is empty; the efficiency number above is for a full airplane, however. Therefore, our estimate needs to be increased to 217 million tons.
Saving only 1% of this would reduce fuel consumption by 2.17 million tons per year, which comes pretty close to the first estimate. This is enough to fill more than 41 Panamax oil tankers (the maximum size for the old Panama canal) or 18 Neopanamax oil tankers.
Or, to look at this from a different angle, with the current price of kerosene of 1.76 USD per gallon, the saved fuel equates to 1.25 billion USD if everyone paid US prices for Jet A-1 fuel. Compared to the average net profit of all airlines per year between 2007 and 2017, which amounts to 13 billion USD, this is almost 10% of yearly profits.
Now this doesn’t look so insignificant any more, does it?

To elaborate on this: 3,119 metric tons of fuel would sell for about 5 million US dollars. So yes, this would be very significant.

I disagree in the sense that such figures are more misleading. Big numbers blow out our human minds, we can't put them into perspective intuitively. The really important figure is still: 1%. Whether it's important or significant is another matter, but it's much easier (and more valid!) to grasp it.

Hm, it actually still doesn't seem like that much to me as a laymen. I feel like airplanes must waste far more fuel than this just due to logistical inefficiencies/preventable delays/etc.

@Zeus: May I offer a different view? The question is "How much would this mean to the industry", and I offered the perspective for the whole industry. Ask anyone in airline operations how significant 1% fuel savings are and their answer would sound like Koyovis. If your mind is blown by big numbers, maybe try to put them into perspective (like I did with the railway car comparison). Or would you prefer an answer along the line of "the numbers are too big to contemplate, so you don't get an honest answer"?

The complex exponential equation results in "1% reduced mass of aircraft means 1% less fuel used".  Which you can pretty much determine via napkin math.  ;)

Is 50,000 cycles realistic? That's five and a half cycles per day, seven days a week for 25 years.

@DavidRicherby: I was afraid the number is too low. There are 737s around with more than 70,000 cycles, and the record holder (Haiwaiian Airlines = very short trips) stands at more than 95,000. The A320 is more recent, but will get there as well.

@Yakk: Right, and napkin math will give you the absolute amount of fuel as well, doesn't it?

No, I'm just amused by the fact both answers used a really complex equation to get that 1% reduction number.  Note that http://www.indexmundi.com/energy/?product=jet-fuel says 5 million barrels/day of all jet fuel consumption.  1% of that is then 50 thousand/day, times 365 is 18 million barrels. At 42 galleons per barrel, and your 1.76$/galleon, that gives us 1.33 billion USD.  However, this was consumption for all uses; some subset of that is used by commercial airlines.  Still, this second derviation validates yours!

@PeterKämpf I think that the last full paragraph of your answer, where you compare cost of the fuel to yearly profits, is really the most meaningful assessment of how much it matters to the industry, and you might consider focusing more on that than on how many tankers and so on. Those absolute numbers/sizes are interesting, and yeah, they're really big, but everything about the whole industry is really big, so they don't give as strong a sense of how much it matters to the industry.

@Jefromi: It is the last paragraph because I added it last. I first had to research the numbers, while the Breguet equation was copied from an earlier answer ;-)

@Yakk: Look at it this way: Both answers use a proven equation to conclude that 1% of weight savings really amounts to 1% of fuel saved. Might be trivial, but that's how engineers think.

@PeterKämpf Right, I'm not surprised it ended up there, but my suggestion was to edit, to try to end up with fewer people thinking what Zeus mentioned.

Is the tanker capacity off? ... tankers are in the 100,000 ton range, so I'd believe 41 Panamax tankers rather than 4,100 ... were you carrying the full fuel requirements rather than just the 1% saving?

@BrianDrummond: Thank you for spotting this. Embarrassingly, I took the full fuel consumption instead of the 1% for the tanker comparison. Corrected.

I took the liberty of adding in a link to the Neopanamax, since I believe this is what the reference to "17" in the penultimate paragraph meant in comparison to the "41" that proceeded it.

One % of takeoff weight is huge. On a B747 with MTOW of 300 tons, that is a weight saving of 3,000 kg, weight that needs not be lugged around for the couple of decades that the aircraft will be flying.
At the aircraft factory where I used to work, there were Idea Boxes everywhere where one could deposit suggestions for weight savings, every kg saved adds to improvement of fuel economy. How much depends on range and a whole lot of other factors, and can be quantified for specific aircraft.
1%. Yuuge.
If we make an estimate for a B747-400 flying maximum range of 12,700 km according to slide 7/14 out of this presentation.

MTOW is given as 400,000 kg, fuel weight as 175,000 kg, this makes $W_{final}$ = MTOW - $W_{fuel}$ = 225,000 kg. With 1% saving, MTOW is reduced to 396,000 kg. Range stays the same if $\frac{W_{init}}{W_{final}}$ stays the same. So the new $W_{final}$ becomes:
$$ W_{final} = \frac{396,000}{400,000}\cdot 225,000 = 222,750 kg$$
$W_{final}$ is again MTOW - $W_{fuel}$ =>
$$W_{fuel} = MTOW - W_{final} = 396,000 - 222,750 = 173,250 kg$$
Final fuel saving is 175,000 - 173,250 = 1,750 kg
For one long distance, maximum range flight, a reduction of 1% in TO weight saves 1,750 kg of fuel. Every percent of weight savings equates to a percent of fuel saved. Every trip, for 2 - 3 decades.

MTOW of 300 tons?  Try 438 tons.

There you go, even Yuger.

Hm, from what I read, taxiing burns 1.5 tons of fuel per 10 mins... whereas this supposedly seems to translate into a 62 kg fuel consumption (from the above answer)? So like, equivalent to ~30 seconds of taxiing? Yet I don't get the impression airlines really care enough to try to minimize the number of seconds to such a granularity. Am I correct, wrong, or missing something?

You take savings from any source you can. Taxiing is necessary anyway, regardless of the MTOW savings. Would you not want to save 62 kg of fuel every trip for 20 years, because you need to spend fuel taxiing?

1,750kg is just 1% of the original fuel weight of 175,000kg. But that assumes the weight is being shaved off of every part of the airplane proportionally, rather than being reduced in one area (i.e. structure) while leaving other areas (i.e. passenger weight) the same.

Again, reasonably complex mathematics that generates the conclusion "reduce aircraft mass by 1% and save 1% fuel".  Which is the kind of conclusion you'd be surprised if it wasn't true.

@Yakk I don't think I'd upvote a question which made the assumption that it was true without justifying it.  So many things don't scale the same in science, and planes are quite complicated balanced pieces of machinery. I think it's very important to demonstrate a justification for assuming they do.

@CortAmmon 100% agreed with you there. Anybody can state anything, and they do. What justifies the statement though? How can we know that fuel quantity used scales linearly with weight, and not for instance quadratically like it does with airspeed?

@TheEnvironmentalist Reduce the payload by 1% and you also save 1% fuel consumption. That is why there are payload-range diagrams.